Abstract: The DC system is the last barrier of the substation power supply system, and its power supply reliability directly affects the operation of the entire substation. Based on a 220 kV substation, using lithium iron phosphate batteries to replace the original lead-acid batteries, this article analyzes the characteristics and applications of lithium iron phosphate batteries advantages and feasibility, studies the topological structure of the DC system, and calculates the short-circuit current of the upgraded DC system. According to the calculation results, and referring to the circuit breaker tripping curve, the paper analyzes the rationality of its level difference coordination, and points out the defects of the converter and the fuse. It provides a basis for the further upgrade and transformation of the DC system.

Key words: DC system, Lithium iron phosphate battery, smart battery parallel system, Level difference coordination